It all really depends on the scale of your conversion. If your simply going to
stick down some floorboards, carpets and give it a lick of paint
then I would suggest that your current stairs will suffice. If your going to
structural alterations or changes to the fabric of the building then you may
need to involve your building officer.

Building regulations are only meant as a means to ensure that building works
are undertaken and completed in such a manner that prevent disasters from
occuring. A building regs officer, unlike his planning counterpart couldn't give
two hoots about what your building or where. Just how your building it and
thats its safe for use and fit for purpose in a multitude of ways.

My suggestion would be to give your local council offices a ring and ask to
speak to someone in the building regulations department. Someone will
always be happy to discuss with you the requirements, if any of your
particular project. They won't ask for your name or anything, just offer
you the right advice. See what they say.